require 'rvg/rvg'

FONT_STYLES = { font_size: 20, font_weight: 'bold', fill: 'white' }

rvg = Magick::RVG.new(450, 150) do |canvas|
  canvas.background_fill = 'white'
  canvas.rect(400, 50, 25, 50)
  canvas.circle(40, 100, 75).styles(opacity: 0.25, stroke: 'blue', fill: '#00ff00', stroke_width: 8)
  canvas.text(83, 83, '0.25').styles(FONT_STYLES)
  canvas.circle(40, 225, 75).styles(opacity: 0.50, stroke: 'blue', fill: '#00ff00', stroke_width: 8)
  canvas.text(208, 83, '0.50').styles(FONT_STYLES)
  canvas.circle(40, 350, 75).styles(opacity: 0.75, stroke: 'blue', fill: '#00ff00', stroke_width: 8)
  canvas.text(333, 83, '0.75').styles(FONT_STYLES)
  canvas.rect(449, 149).styles(fill: 'none', stroke: 'blue')
end

rvg.draw.write('rvg_opacity.gif')
